Occupant comfort, health, and safety in contemporary buildings are dependent on a wide variety of factors, such as the proper management of space temperature, space humidity, and fresh air ventilation rate, as well as the related accumulation of pollutants, such as carbon dioxide (CO2) or volatile organic compounds (VOCs). Many different combinations of air-conditioning systems are installed in modern buildings to meet this range of requirements. Unfortunately, a number of difficulties often arise when different combinations of heating, cooling, and ventilation systems are used for conditioning the same space.
One example of such a combination of multiple space-conditioning systems is the combination of a dedicated outdoor air system (DOAS), used to meet the latent load imposed by the fresh ventilation air, and a parallel cooling system, such as a variable refrigerant flow (VRF) system, which is used to meet the sensible load of the indoor air. These systems typically operate concurrently to manage the total heating/cooling load and supply needed ventilation air to the occupied space. Each of these systems is often designed and controlled independently, and treats the operation of other systems as disturbances. Such control strategies make it difficult to operate the equipment in a reliable and energy efficient manner.
For example, U.S. Pat. No. 7,669,433 discloses a multi-air conditioner central control system that creates a schedule for coordinated operation of different air-conditioning systems including both vapor compression cycles and ventilation systems that do not include refrigerant-containing elements. However, the communication and operation of the combined system does not teach how to operate the combination of systems to achieve some desired performance for the systems. For example, a DOAS may control the supply air temperature to a given setpoint, while the VRF system may be designed to regulate the temperature of the space to a different specified setpoint. In this case, a VRF system that is not operated in consideration of the performance of the DOAS system may cause dynamic system cycling losses, temperature fluctuations, and commensurately low system-level energy efficiency. Though this prior art does not include refrigerant-containing components in the ventilation system, the addition of a second vapor compression cycle to the ventilation system introduces numerous additional degrees of freedom into the integrated system. While this increases the potential performance of the resulting overall system, it also can make the efficient operation of the combination of systems more difficult to achieve.